[ffi] Avoid overloading Value struct

[alarso16]

Currently, the ffi/memory.go file handles all translation between C and Go memory correctly, but it's extremely unreadable for newer contributors, and is difficult to verify correctness by reading it. An offline discussion resulted in the following ideas:

• Leave it as is (readable enough)
• Use Rust-style syntax to wrap with a Go struct (see Use a Value go type to consolidate #920)
• Create a new struct in Rust for each return type, even if they contain the same underlying data.

[demosdemon]

I'm curious if c-for-go would be useful here to autogenerate our c bindings.

[rkuris]

@demosdemon I think this is done. Close if so.

[demosdemon]

@demosdemon I think this is done. Close if so.

It is not. There is a linked PR.